fix: --run-batches --runner claude silently falls through to codex subprocess

[dmg604]

Problem

When --run-batches --runner claude is used, _select_batch_runner in batch/orchestrator.py silently falls through to run_codex_batch, which spawns a codex subprocess. In environments where codex is not available (e.g. Claude Code sessions), this produces a silent failure or cryptic error with no guidance on the correct workflow.

Expected behavior

--runner claude should fail fast with a clear error explaining that Claude is not a subprocess runner and describing the correct workflow.

Correct workflow for Claude

desloppify review --run-batches --dry-run
# launch one subagent per prompt file in .desloppify/subagents/runs/<run>/prompts/
# each writes JSON to results/batch-N.raw.txt
desloppify review --import-run <run-dir> --scan-after-import

Fix

In _select_batch_runner, add a claude case that raises CommandError with the correct instructions instead of falling through to run_codex_batch:

if normalized == "claude":
    raise CommandError(
        "The 'claude' runner does not spawn subprocesses. "
        "Use --run-batches --dry-run to generate prompt files, "
        "launch one subagent per prompt file, write JSON output to "
        "results/batch-N.raw.txt, then import with "
        "--import-run <run-dir> --scan-after-import.",
        exit_code=1,
    )

5810 existing tests pass with this change applied.